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Synlett 2006(4): 0621-0623  
DOI: 10.1055/s-2006-926248
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Pyranonaphthoquinone Antibiotics Involving the Phthalide Annulation Strategy

Sven Claessensa, Dashnie Naidoob, Dulcie Mulhollandb, Luc Verschaevec, Johannes van Stadend, Norbert De Kimpe*a
a Department of Organic Chemistry, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium
Fax: +32(9)2646243; e-Mail: norbert.dekimpe@UGent.be;
b School of Chemistry, University of KwaZulu-Natal, Howard College Campus, 4041 Durban, South Africa
c Department of Environmental Toxicology, Vito (Flemish Institute for Technological Research), Boeretang 200, 2400 Mol, Belgium
d Research Centre for Plant Growth and Development, School of Botany and Zoology, University of Natal, Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa
Further Information

Publication History

Received 24 November 2005
Publication Date:
20 February 2006 (online)

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Abstract

The synthesis of the pyranonaphthoquinone antibiotic pentalongin was performed using the phthalide annulation strategy. Annulation of the cyanophthalide onto 6H-pyran-3-one resulted in a hongconin analogue, which upon further elaboration was converted into the natural product.

Key words

annulations - natural products - quinones - phthalide - pentalongin

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Van Puyvelde, L.; Hakizayezu, D.; Brioen, P.; De Kimpe, N.; De Vroey, C.; Bogaerts, J.; Hakizamungu, E., presented at International Congress on Natural Products Research, July 31 to August 4, 1994; Halifax, Canada, 1994.

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De Kimpe, N.; Kesteleyn, B.; Nguyen, Van T.; Van Puyvelde, L. 18th International Congress of Heterocyclic Chemistry, July 29 to August 3, 2001; Yokohama, Japan, 2001, 120.

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5,10-Dimethoxy-1 H -benzo[ g ]isochromene-4-one ( 13): yellowish oil; 1H NMR (acetone-d 6): δ = 3.90 (3 H, s, OCH3), 4.01 (3 H, s, OCH3), 4.30 (2 H, s, CH2C=O), 5.06 (2 H, s, CH2O), 7.62 (1 H, ddd, J = 8.4, 7.0, 1.4 Hz, CH-7), 7.73 (1 H, ddd, J = 8.4, 7.0, 1.4 Hz, CH-8), 8.11 (1 H, dd, J = 8.4, 1.4 Hz, CH-9), 8.34 (1 H, dd, J = 8.4, 1.4 Hz, CH-6). 13C NMR (acetone-d 6): δ = 62.13 (OCH3), 63.14 (OCH3), 64.46 (CH2O), 74.50 (CH2OC=O), 118.30 (Cquat), 122.01 (CH-9), 125.05 (CH-6), 126.84 (CH-7), 127.45 (Cquat), 129.08 (Cquat), 129.74 (CH-8), 131.74 (Cquat), 146.43 (Cquat), 155.64 (Cquat), 193.47 (C=O). IR (KBr): νmax 1689 (C=O) cm-1. MS (ES+): m/z = 258 [M+].

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4-Hydroxy-3,4-dihydro-1 H -benzo[ g ]isochromene-5,10-dione ( 6): 1H NMR (CDCl3): δ = 3.86 (1 H, dd, J = 12.2, 3.8 Hz, CHCH a Hb), 4.03 (1 H, dd, J = 12.2, 3.5 Hz, CHCHa H b ), 4.49 (1 H, dd, J = 18.9, 1.65 Hz, OCH a Hb), 4.76 (1 H, dd, J = 18.9, 0.6 Hz, OCHa H b ), 4.82 (1 H, m, CHOH), 7.76 (2 H, m, CH7-CH8), 8.09 (2 H, m, CH6-CH9). 13C NMR (CDCl3): δ = 60.18 (CH2O), 63.23 (CHOH), 69.51 (CH2), 126.38 (C-6 or C-9), 126.63 (C-9 or C-6), 131.83 (2 × Cquat), 134.28 (C-7 and C-8), 140.58 (Cquat), 143.74 (Cquat), 183.84 (C=O), 184.59 (C=O). IR (KBr): νmax = 3468 (OH), 1661 (C=O) cm-1. MS (ES+): m/z (%) = 231 (15) [M + H+], 213 (100) [M+ - H2O].